It comes nearly a year after the Pentagon unveiled a policy that opened 14,000 new jobs to women, but continued to prohibit them from serving in infantry, armour and special operations units whose main function was to engage in frontline combat.

Australia's Defence Minister Stephen Smith announced in late 2011 that the Australian Army would allow women to serve in combat roles within five years.

Lines blurred

Calls to lift the US Army's blanket prohibition have mounted after more than 10 years of war in which women fought and died in counter-insurgency campaigns in Iraq and Afghanistan, where front lines were blurred.

Some senior officers have privately voiced concerns that infantry and special forces units require major upper body strength and that difficult physical tests should not be relaxed for female recruits.

But female veterans and activists say they are only demanding an equal chance to apply for combat jobs - and not any special treatment.

Women make up about 14.5 per cent of the active duty US military, or about 204,000 service members, according to the Pentagon.

About 2 per cent of US deaths in Iraq and Afghanistan have been women.

Around 280,000 women have been deployed to the war zones over the past decade, about 12 percent of the US total.

Mr Panetta's decision would apply mainly to the Army and the Marine Corps, as the Air Force and Navy already have lifted most prohibitions on women in combat, with women flying warplanes and launching weapons on ships.

In 2010, the Navy opted to allow women to serve on submarines.

The move has been welcomed by US senator Carl Levin, the head of the Senate Armed Services Committee.

He says it reflects the "reality of 21st century military operations".

The American Civil Liberties Union, which had filed a suit in November seeking to force the Pentagon to end the ban, has also praised the decision.

Free trade is the oldest argument in federal politics and the issue that literally defined the federation era but opposition exists to the TPP, courtesy of the Investor-State Dispute Resolutions clause.